1. Field of the Invention
The present invention relates to a hard disk drive, and more particularly, to an actuator latch mechanism for a hard disk drive, which locks an actuator in a predetermined position when a disk is stopped from rotating, so as to prevent the actuator from drifting due to an external shock.
2. Description of the Related Art
A hard disk drive reads data from and/or writes data on a disk using a read/write head. During the reading and writing operations, the head is shifted to a desired position on the surface of the disk by an actuator, while flying over the recording surface of the spinning disk at a proper height.
When the hard disk drive is not operating, in other words, when the disk is stationary, the head needs to be parked in a position separated from the recording surface of the disk so that the head does not collide with the recording surface of the disk. Such a parking system of the head is mainly classified into a contact start stop (CSS) mode and a ramp load/unload mode. In the CSS mode, a landing zone in which data is not recorded is provided in an inner periphery of the disk, and the head is parked in the landing zone, with the head being in contact with the disk. Meanwhile, in the ramp load/unload mode, a ramp is provided outside of the disk, and the head is parked on the ramp.
However, even when the head is parked in the landing zone of the disk or on the ramp, the actuator may drift by an external shock or vibration, and thus, the head may be shifted toward the recording surface of the disk when separating from the landing zone or the ramp. As a result, the head contacts the recording surface of the disk, and the head and the recording surface of the disk may be damaged. Accordingly, it is necessary to lock the actuator in a proper position, when the disk is stationary and the head is parked in the landing zone or on the ramp. To this end, various actuator latch mechanisms have been proposed.
FIGS. 1A, 1B and 1C show an inertial latch mechanism, which is one example of a conventional actuator latch mechanism of a hard disk drive.
Referring to FIG. 1A, the hard disk drive is provided with an actuator 10 moving a read/write head to a desired position on the disk. The actuator 10 includes a swing arm 12 rotatably coupled to a pivot bearing 11, and a suspension 13 installed at one end portion of the swing arm 12 supporting and biasing a slider 14, on which the head is mounted, toward the surface of the disk.
The hard disk drive is also provided with an inertial latch mechanism 20 locking the actuator 10 while the head is parked on a ramp 15. The inertial latch mechanism 20 includes a latch lever 21 pivoted by inertia, a latch hook 22 provided to a front end of the latch lever 21, a notch portion 23 formed on the swing arm 12 of the actuator 10, a crash stop 24 restricting a clockwise rotation of the swing arm 12, and a latch stop 25 for restricting a clockwise pivoting movement of the latch lever 21.
If the hard disk drive receives a clockwise directional shock, the swing arm 12 of the actuator 10 and the latch lever 21 are pivotally rotated in a counterclockwise direction by inertia, as shown in FIG. 1B. Thus, the latch hook 22 engages the notch portion 23, thereby restricting further rotation of the swing arm 12 of the actuator 10. On the contrary, if the hard disk drive receives a counterclockwise directional shock, the swing arm 12 of the actuator 10 and the latch lever 21 are pivotally rotated in a clockwise direction by inertia, as shown in FIG. 1C. At this time, the swing arm 12 is firstly rotated in the clockwise direction until it abuts the crash stop 24. The swing arm 12 is rebounded by the collision, and is thus rotated in the counterclockwise direction. Also, the latch lever 21 is rebounded by the collision between the latch lever 21 and the crash stop 25, and is thus pivoted in the counterclockwise direction. As such, the notch portion 23 is interfered with the latch hook 22 to lock the actuator 10.
However, the conventional inertial latch mechanism 20 described above may operate only by a relatively strong shock, enough to pivot the latch lever 21. Specifically, there is a problem in that if a relatively light shock or vibration is applied to the hard disk drive, the latch lever 21 operated by inertia is not rotated, and thus, the actuator 10 is not locked and drifts. Accordingly, when a light shock is applied to the hard disk drive, it is difficult to reliably lock the actuator 10.
FIGS. 2A and 2B show another actuator latch mechanism addressing the above drawback.
Referring to FIG. 2A, an actuator 30 of a hard disk drive is provided with a voice coil motor (VCM) rotating a swing arm 32. The voice coil motor includes a VCM coil 37 coupled to a rear end portion of the swing arm 32, and a pair of magnets 38 each disposed at an upper portion and at a lower portion of the VCM coil 37 in such a way that the magnets 38 face the VCM coil 37.
An actuator latch mechanism 50 shown in FIGS. 2A and 2B is constructed to lock the actuator 30 by a magnetic flux of the magnet 38, as well as an inertial force. For this purpose, the latch mechanism 50 includes a notch portion 51 formed at an end portion of the swing arm 32, and a latch lever 54 pivotally supported around a pivot shaft 55. The swing arm 32 is provided at the end portion thereof with a first iron core 53 applying a magnetic force between the magnets 38 and the swing arm 32. The first iron core 53 generates a torque to rotate the swing arm 32 in the clockwise direction by the magnetic flux of the magnets 38. The latch lever 54 is provided at one end thereof with a hook 56 to engage the notch portion 51, and at the other end thereof with a second iron core 57 to generate a magnetic force due to the magnets 38. The second iron core 57 generates a torque to pivotally move the latch lever 54 in the clockwise direction by the magnetic flux of the magnets 38. The clockwise pivoting movement of the latch lever 54 due to the torque is restricted by the latch stop 59.
The conventional latch mechanism 50 operates as follows. When the head mounted on the slider 34 is parked on the ramp 40, the swing arm 32 is rotated in the clockwise direction around the pivot bearing 31 by the voice coil motor. At that time, the swing arm 32 pushes the latch lever 54, and so the latch lever 54 is pivoted in the counterclockwise direction. The rotation of the swing arm 32 is stopped at the position where the flux generated from the magnets 38 and the magnetic force generated by the first iron core 53 provided to the swing arm 32 are maximum, and thus, the pivoting movement of the latch lever 54 is stopped. Therefore, as shown in FIG. 2A, the process of parking the head is completed, and simultaneously, the actuator is locked by the latch mechanism 50.
As described above, if the hard disk drive receives a clockwise rotational shock higher than the magnetic force acting between the first iron core 53 and the magnets 38, the swing arm 32 and the latch lever 54 are pivotally moved in the counterclockwise direction by inertia. Accordingly, the hook 56 of the latch lever 54 engages the notch portion 51, thereby restricting further pivoting movement of the swing arm 32 of the actuator 30. On the contrary, if the hard disk drive receives a counterclockwise rotational shock, an inertial torque in the clockwise direction is exerted on the swing arm 32 and the latch lever 54. As shown in FIG. 2A, however, the swing arm 32 is in contact with the latch lever 54, so that the clockwise pivoting movement does not happen.
Meanwhile, if the hard disk drive drives with a light external shock lower than the magnetic force acting between the first iron core 53 and the magnets 38, the swing arm 32 is not pivoted by the magnetic force.
As such, since the actuator latch mechanism 50 utilizes both a magnetic force and inertia, it is possible to reliably lock the actuator for a relatively light shock and vibration, as well as a strong external shock.
Next, referring to FIG. 2B, in order to operate the hard disk drive, the head has to be shifted from the ramp 40 to the recording surface of the disk. To this end, the locking state of the actuator 30 has to be released. At this time, if power is applied to the VCM coil 37 provided at the rear end portion of the swing arm 32, the swing arm 32 overcomes the magnetic force acting between the magnets 38 and the first iron core 53 provided to the swing arm 32, i.e., the latching force, and is thus rotated in the counterclockwise direction. Simultaneously, the latch lever 54 is pivoted in the clockwise direction by the magnetic force acting between the magnets 38 and the second iron core 57, so that the notch portion 51 of the swing arm 32 does not interfere with the hook 56 of the latch lever 54.
In the conventional actuator latch mechanism 50 described above, the magnet 38 typically is shaped to face only the portion of the VCM coil 37 perpendicular to the rotational direction of the swing arm 132. Accordingly, there is a drawback in that the clockwise torque applied to the latch lever 54 is small since a distance between the shaped magnet 38 described above and the second iron core 57 provided at the latch lever 54 is relatively long, and thus, the magnetic flux of the magnets 38 acting on the second iron core 57 is not large. In this case, when the locking state of the actuator 30 is released, the clockwise rotation speed of the latch lever 54 is not faster than that of the counterclockwise rotation of the swing arm 32. As such, the notch portion 51 of the swing arm 32 engages the hook 56 of the latch lever 54.
In order to solve the above problem, the swing arm 32 has to be slowly rotated. However, it is very difficult to slowly rotate the swing arm 32 because a rotational speed of the swing arm 32 is controlled using back electromotive force (back-EMF) generated from the VCM coil 37. If the rotational speed of the swing arm 32 is low, the back electromotive force becomes small. As such, it is very difficult to control the rotational speed of the swing arm 32.